For example, Japanese Laid-Open Patent Publication No. H1(1989)-150065 discloses such a power transmission, which comprises a continuously variable ratio-change mechanism and a fixed ratio rotational transmission mechanism. The power transmission disclosed in this publication further comprises a torque converter, which receives the rotational driving force of an engine. The gear train (a gear type rotational transmission mechanism or a fixed ratio rotational transmission mechanism) and the belt type continuously variable ratio-change mechanism are arranged in parallel with each other between the input shaft and the output shaft of the transmission, with the input shaft of the transmission being connected with the output shaft of the torque converter and the output shaft of the transmission being connected rotationally to the drive wheels of a vehicle.
FIG. 11 shows the arrangement of power transmission members of the transmission disclosed in the above mentioned Japanese Laid-Open Patent Publication No. H1(1989)-150065. The drive pulley 501 of the belt type continuously variable ratio-change mechanism is disposed on the input shaft, whose rotational axis is marked with O11 in the drawing, and the driven pulley 502 is disposed on a middle shaft, whose rotational axis is marked with O12. A V belt 503 is disposed around these pulleys. By adjusting the widths of the pulleys 501 and 502, the speed change ratio of the transmission is varied continuously without any step. The rotation of the driven pulley 502, whose speed is changed in this way, is then transmitted from an output drive gear 510, which is disposed on a middle shaft, to an output driven gear 511, which meshes with the output drive gear 510. The output driven gear 511 is disposed on an output shaft, whose rotational axis is indicated with O13.
Additionally, the input shaft is provided with a forward low drive gear 505, which meshes with a forward low driven gear 506 disposed on the output shaft, whose rotational axis is O13. With this gear train, the transmission is set in a forward low speed ratio mode. In addition, the input shaft is provided also with a rearward drive gear 507, and this drive gear 507 meshes with a rearward idler gear 508, which meshes with the above mentioned output driven gear 511. With this gear train, the transmission is set in a rearward rotation mode. Furthermore, the output shaft is provided with a final drive gear 515. This gear meshes with a final driven gear 516, which is integrally provided in a differential mechanism, whose rotational axis is O14. With this arrangement, the rotational driving force transmitted to the output shaft with a rotational speed change is then transmitted through the final drive and driven gears 515 and 516 to the drive wheels of the vehicle.
Also, Japanese Laid-Open Patent Publication No. 2002-48213 discloses a power transmission that comprises a belt-type continuously variable ratio-change mechanism and a fixed ratio rotational transmission mechanism. In this transmission, the belt type continuously variable ratio-change mechanism and the fixed ratio rotational transmission mechanism are disposed in parallel with each other between the input shaft and the output shaft of the transmission, the input shaft being connected through a damper to an engine. The fixed ratio rotational transmission mechanism is equipped with a forward/reverse-switching mechanism, which comprises a planetary gear train disposed on the input shaft. The planetary gear train comprises a forward (starting) clutch and a reverse brake, which are used for switching the mode of the transmission between forward drive and reverse drive. In addition, a direct coupling clutch is provided on the input shaft for establishing the power transmission through the belt type continuously variable ratio-change mechanism.
In designing a power transmission that combines a continuously variable ratio-change mechanism and a fixed ratio rotational transmission mechanism, there are many possible arrangements for disposing these two mechanisms in parallel. Therefore, it is important to consider how efficiently and compactly they are integrated in the transmission.
Optimal arrangement should provide a high degree of freedom in positioning components while satisfying, for example, a range of speed change ratio, a maximum ratio and a minimum ratio that are required for the transmission. Yet, the transmission should be as small and compact as possible.
It is also important to position compactly the clutching means that switches the power transmission between the continuously variable ratio-change mechanism and the fixed ratio rotational transmission mechanism and the clutching means that switches the power transmission by the fixed ratio rotational transmission mechanism between its forward drive and reverse drive.
Furthermore, since the drive pulley and the driven pulley, which constitute the continuously variable ratio-change mechanism, and members that constitute the oil chambers for the drive and driven pulleys, respectively, have larger outer diameters, it is important to place these components compactly together with the fixed ratio rotational transmission mechanism.
From these points of view, the arrangement of the transmission disclosed in the above mentioned Japanese Laid-Open Patent Publication No. H1(1989)-150065 has a problem of not having a high degree of freedom for the above mentioned forward low drive gear 505 and driven gear 506 of the transmission, which define a forward low speed change ratio, i.e., a large speed change ratio (speed reduction ratio), requiring the diameter of the forward low drive gear 505 to be comparatively small and that of the forward low driven gear 506 to be comparatively large. Especially, it is difficult to make the diameter of the forward low drive gear 505 small since the forward low drive gear 505 is disposed on the input shaft, with the diameter of the forward low drive gear 505 being larger than that of the input shaft. As a result, the diameter of the forward low driven gear 506 is correspondingly large, contributing to the enlargement of the transmission. Moreover, because the distance between the input shaft and the output shaft is determined by these two gears that mesh with each other, there is not much freedom in positioning these shafts, and there is little freedom in deciding the position of the output shaft with respect to the input shaft.
In the arrangement of the transmission disclosed in the above mentioned Japanese Laid-Open Patent Publication No. H1(1989)-150065, which is shown in FIG. 11, the drive pulley of the belt type continuously variable ratio-change mechanism, a forward low clutch that establishes a forward low speed ratio, and a reverse clutch that establishes a reverse speed ratio are disposed in parallel with one another on the input shaft. As a result, the input shaft is relatively long in its axial direction, so the protrusion of the part of the transmission where the input shaft is incorporated is remarkable. This condition makes it difficult for the transmission to achieve a high degree of compactness. Similarly, in the case of the above mentioned transmission disclosed in Japanese Laid-Open Patent Publication No. 2002-48213, the drive pulley, the forward/reverse switching mechanism, which comprises a planetary gear train, the friction (starting) clutch, the rearward brake, and the direct coupling clutch are all disposed in parallel with one another on the input shaft. As a result, the part of the transmission where the input shaft is incorporated is a major cause that enlarges the transmission axially as well as radially. This is a problem that makes it difficult for the transmission to achieve a high degree of compactness.